In a wide variety of applications it is advantageous or necessary to sense the position of a linearly or rotationally movable element. For example, in automobile seat applications the seat may be linearly movable, either manually or automatically via electromechanical means, on an associated track assembly. A sensor may provide a signal representative of the linear position of the seat on the track for a variety of purposes, e.g. to control deployment of an air bag, to control the electromechanical actuator that causes translation of the seat in connection with a seat position memory feature, etc.
For a seat position application, it is increasingly desirable for a sensor to provide multiple position outputs for purposes of ascertaining occupant position. For example, in applications where seat position is used to control air bag deployment early configurations involved only single stage air bag systems. A single stage air bag deploys with a known deployment force that may not be varied. In this application, seat position information was used only to determine when the airbag should be deployed. However, the advent of dual stage air bags, i.e. air bags that may be deployed with two distinct deployment forces, required increased resolution in position sensing. Also, the industry is now moving to variable stage airbags where the deployment force may be varied depending upon occupant position and classification. Variable stage airbag configurations will require a sensor that can detect multiple seat positions for use in determining the appropriate deployment force.
Another desirable feature of a position sensor, especially in the context of an automobile seat application, is that it be non-contact. A non-contact sensor has a sensing element that does not physically contact the sensed object. It is also advantageous that the sensor be mechanically decoupled from the seat track in an automobile seat application. These features allow quiet operation of the sensor and minimize wear, which could cause deterioration of performance.
Another difficulty associated with seat position sensors is that the seat track environment is very crowded, e.g., there is limited physical space for such sensors. Also the space available for the sensor may vary from among vehicle types. The size and packaging of the sensor should, therefore, be flexible to allow use in a variety of vehicle types. In addition, it would be advantageous to have a menu of sensor configurations to allow selective use of an appropriate configuration depending on the track environment.
Accordingly, there is a need for a non-contact position sensor that provides accurate and reliable position sensing that may be cost-effectively produced and installed.